If model uses [composed_of](http://apidock.com/rails/ActiveRecord/Aggregations/ClassMethods/composed_of) to convert an attribute to manipulate the value of the attribute symantic_form_for may not present the value of the field properly. 

Here is an example of how to add money money (using [money gem](https://github.com/RubyMoney/money))

    # encoding: utf-8

    module Formtastic
      class SemanticFormBuilder

        def money(method, options = {})
          value = object.send(method).format(:no_cents_if_whole => true, :symbol=>false)
          new_input_html = options[:input_html] ? {:value=>value}.merge(options[:input_html]) : {:value=>value}
          options[:input_html]=new_input_html
          input(method, options)
        end
      end

    end

After that, you can use form.money as any other input

    <%= semantic_form_for @new_rate || Rate.new() do |form| %>
        <%= form.money :value %>
    <% end %>
